Method of greaseproofing porous materials



' Oct. 19, 1943. A. Ai RGBBINS 2,332,1 9

Filed Feb. 6. 1939 FIG. .2.

wmx xmw INVENTOR. A; Z5274 E ale/N5 BY 1 ATTORNEY.

Patented Oct 19, 1943 I METHOD OF GREASEPROOFING POROUS MATERIALS Albert A. Robbins, Berkeley, Calif.

Application February 6, 1939, Serial No. 254,895

13 Claims.

My invention relates to a method of preparing grease-proof material from porous materials and has particular reference to a method'of treating paper, fabrics, or other similar materials to render them substantially impervious to liquids,

and finds particular utility in the preparation of paper from which paper containers are made.

It is very often desirable and necessary to prepare porous materials in such fashion as to render them impervious to liquids and particularly to render them impervious to oily or greasy liquids.

One of the common uses to which porous materials are put is the manufacture of paper containers in which relatively porous cellulose paper is used to form a container, the walls of which are made up of either single or multiple layers of the paper. When such a container is used for the packaging of liquids comprising either aqueous solutions or oily liquids, or for the packaging of solid ingredients containing absorbed liquids or greasy constituents, it has been found that the liquid content of the package rapidly escapes through the pores in the paper. In cases where the package is used for the actual packaging of liquids this can not be tolerated since in a relatively short time the entire contents of the package have escaped therefrom. When the package is used to enclose solid materials carrying absorbed liquids, the escape of the liquid or greasy constituents seeps or dries out the packaged ma-' terial and spoils the exterior appearance of the package because of the stains resulting from the greasy constituents which pass through the pores. of the paper.

Numerous attempts have been made in the past to provide a method for treating paper which will render it liquid and grease-proof. These attempts have, in most part,, been futile and those'attempts which have been successful are impractical either because of the expense in curred in the practice of the method or because the resulting product is so fragile as to be unable to withstand normal handling without fracturing the coating employed and thereby destroying the grease-proofing qualities.

One of the oldest and most commonly attempted method of grease-proofing porousmaterials comprised the use of viscose as a meansof obtaining regenerated cellulose whose inherent grease-proofing properties have long been well known. These attempts have in general been of two types, either attempts at providing a very thin flexible surface film of regenerated cellulose on the material to be treated or attempts at total impregnation of the material with viscose. Theestablishment of a thin surface film has been up to the present time considered practically impossible since in order to derive the required flexibility, the film must be made so thin as to render it impossible to establish a continuous, unbroken film. Attempts to accomplish this in the past have failed because no one has been able to provide on a fabric a film of sufficient thinness which is continuous and without porosity or breaks. I

The attempts to grease-proof porous material by totally impregnating the material with viscose have also been unsuccessful because the material so treated became, upon drying, so hard, brittle and 'unflexible as to render it absolutely unfit for later use in the fabrication of cartons, containers or other devices.

It is therefore an object of my invention to provide a method of grease-proofing porous materials which establishes a surface film on the material which is flexible and has great strength and wear-resisting qualities.

It is also an object of my invention to provide a method of grease-proofing of the character set forth in the preceding paragraph which establishes upon the surface of the material treated an unbroken, flexible film of regenerated cellulose.

It is an additional object of my invention to provide a method of the character set forth in the preceding paragraphs for establishing upon the surface of a treated material an unbroken, flexible film of regenerated cellulose secured to the material with a flexible adhesive or bonding agent.

A further object of my invention resides in the provision of a method of grease-proofing porous materials which establishes upon the surface of the material an unbroken, flexible film of regenerated cellulose secured to the material by means of a flexible adhesive and by interposing between the adhesive and the regenerated cellulose a thin film of acetylated cellulose.

It is also an object of my invention to provide a method of preparing a multiple layer of greaseproof material by securing a plurality of sheets of porous materials to each other by means of a grease-proof adhesive.

It is an additional object 'of my invention to provide a method of preparing a multiple layer grease-proof material of the character set forth in the preceding paragraph in which the sheets of porous material are secured to each other by means of regenerated cellulose and a grease-proof adhesive.

It is a further object of my invention to provide a method of preparing a multiple layer grease-proof material in the manner set forth proofing materials comprising the establishment of a surface film of regenerated cellulose and the precipitation of metallic soaps in pores of this surface film.

It is also an object of my invention to provide a metallic soap treatment for moistureproofing porous materials in the manner set forth in the preceding paragraph in which the chemical reaction causing the precipitation of the metallic soap takes place in the regenerated cellulose pores of the material to be moistureproofed.

It is also an object of my invention to provide a method of manufacturing grease-proof tubular containers" from porous materials by impregnating the porous material with viscose and forming the impregnated material into a tubular carton while the viscose is in a plastic stage.

Other objects and advantages of my invention will be apparent from a study ,ofthe following specification, read in connection with the accompanying drawing, wherein:

Fig, l is a greatly enlarged fragmentary crosssectional view of superimposed sheets of porous material after they have been treated and secured to each other by the method of my invention as employed in the manufacture of paper containers and illustrating the relative positions of the various materials employed and the relative positions of the various sealing layers; and

Fig. 2 is a view similar to Fig. 1 illustrating the relationship between the treatment layers and a. sheet of porous material when an alternate method of treatment of my invention is employed to grease-proof a single sheet of such material.

I prefer to employ my method of treatment in the manufacture of paper containers and the preferred embodiment of my invention as incorporated in this manufacturing process may be briefly described as comprising the following steps:

(1) Initially preparing the paper stock by applying to one or both surfaces thereof a relatively thin layer of viscose or by impregnating the pa? per stock with viscose to provide unbroken surface films thereon;

(2) Partially regenerating the viscose surface films to provide surface layers of pure regenerated cellulose thereon;

(3) Winding two or more sheets prepared in this fashion on the well known mandrel of a tubular container forming machine to mold the sheets into a container at a time prior to the setting and hardening of the viscose layers;

' (4) Applying to the adjacent surfaces of the superimposed sheets as they are fed to the container forming machine a suitable adhesive for securing the superimposed sheets to each other, said adhesive comprising a vehicle carrying a nitrating or acetylating agent which reacts with the cellulose films to provide films of acetylated cellulose or nitrated cellulose between the viscose films and the adhesive films;

(5) Completely regenerating the remaining viscose while the sheets are bonded together; 5 (6) Washing the regenerated cellulose thus obtained;

('7) Applying to the exposed surfaces of the carton after it has been removed from the container forming machine an aqueous. solution of the alkaline soaps of the fatty acids;

(8) Adding to the applied soap solutions a aqueous solution of a metallic salt to precipitate insoluble metallic soaps in the pores of the regenerated cellulose to provide impermeable non-porous surfaces on the carton which are substantially impervious to vegetable and mineral oils and greases, water, petroleum hydro-carbons, the alcohols and which are also strongly resistant to dilute acids. I Whenever the term viscose is used herein it shall be understood to refer to the well known substance used in the rayon industry comprising a basic solution of soda-cellulose-xanthate.

More particularly stated, the term "viscose is applied to that product which is obtained by dissolving mercerized cellulose in carbon-bi-sulphide to obtain the compound known as sodacellulose-xanthate, then dissolving the xanthate in a dilute base such as sodium or potassium hydroxide having a concentration of from .three to ten percent.

Referring to Fig. 1, I have illustrated super imposed sheets of paper or other porous materials l and 2 upon the surfaces of each of which may be applied, by any suitable method, relatively thin surface layers 3 and 4 of viscose. The

surface layers are preferably obtained by completely impregnating the sheets I and 2 with viscose. After the establishment of the viscose 40 layers 3 and l, the adjacent surfaces of the layers 3 are partially regenerated to provide very thin films of pure regenerated cellulose.

. The viscose outer exposed surface may be partially or wholly regenerated by any one of a number of methods. In the preferred method,

I partially regenerate these layers by the combined application of heat and relatively dry air,

ers and the dry air acting to carry off the water contents of the viscose, or resulting from the chemical regeneration of the viscose into pure regenerated cellulose. The partially heat regenerated cellulose may, if desired, be then washed with water to remove all or a portion of the residual sulphur compounds.

While I prefer to employ this method because 'of its simplicity and ease of application to manufacturing processes, this partial regeneration may be accomplished by a number of other known methods such as the application of dilute acids or metallic salts such as sulphuric or hydrochloric acids, sulphates or chlorides of sodium, potassium or similar alkaline metals or by treating the surface with ammonium sulphate or ammonium chloride with subsequent exposure to an alkali salt with an acid.

I have found it necessary when this method of partial regeneration is employed to thoroughly wash the regenerated cellulose films after the regeneration to remove any of the "excess acids or salt solutions and any of the products resulting from the chemical reaction taking place on the surface of the films.

The viscose films may also be regenerated by the heat acting to partially regenerate the lay-' aging in which the films must be carefully washed to remove the free sulphur and sulphur compounds which are normally present in the viscose, since the presence of these compounds in the completed container gives rise to the tainting of foods if the container is employed for this purpose. Furthermore, if the container is to be used for the packaging of lubricating oils, the packaged oil would absorb the sulphur compounds and thus spoil the lubricating oil since, as is well known, the presence of sulphur or sulphur compounds in lubricating oils causes the formation of sulphuric or sulphurous acids when the oil breaks down under heat with great resultant damage to the mechanism with which the lubricating oil is used.

After the surfaces of the sheets of paper i and 2 have received the films of viscose 3 and 4 and the surfaces of the adjacent films 3 have been partially regenerated in any of the manners just described, the container forming machine. One of the common methods of manufacture of, tubular paper containers comprises of paper onto a cylindrical mandrel in such a manner that the strips of paper are spirally wound one upon the top of the other in a staggered relationship to provide a-paper tube having walls comprising two or more paper layers.

It is common practice to apply glue or other adhesive between each of the pairs of multiple layers for securing these layers to each other.

I accordingly prefer to apply an adhesive film 5 in a position disposed between the adjacent films 3 in a continuous manner as the sheets i and 2 are fed onto the mandrel of the carton forming machine. I employ the adhesive film 5 not only as an adhesive for securing the superimposed sheets i and 2 to each other, but as a vehicle for carrying an acetylating or nitrating agent such as dilute acetic acid or dilute nitric acid, which agents react with the partially regenerated cellulose film forming the exposed surfaces of the adjacent films 3 to provide thin films 6 and I of acetylated cellulose or nitrated cellulose, depending upon whether an acetylating agent or a nitrating agent is carried by the adhesive 5.

In the preferred embodiment of my invention I prefer to use an acetylating agent such as acetic acid or an acetate salt to the use of a nitrating agent since by this means I form. the films 6 and I of acetylated cellulose, a flame resistant product, whereas the employment of a nitrating agent makes these films of nitrated cellulose, a more inflammable substance. Furthermore, the acetylating agents are substantially non-poisonous so that the use of such an agent renders my method much more p'ractica-' ble as regards factory production methods since the factory employees engaged in "the performance of my method are-much better protected against acid poisoning and chemical injury I have found that animal glue forms a very satisfactory adhesive and. vehicle for providing the adhesive film 5 and carrying the acetylating agent, and while various otherglues such as vegetable glue or synthetic adhesive or mixtures thereof which are soluble in or miscible with the acetylating agent used may be employed, I find feeding two or more strips -to make a film 5 which is in itself inherently grease-proof and flexible to a considerable extent.

The carton thus obtained, the walls of which are composed of superimposed layers of viscoseimpregnated paper separated from each other by alternate layers of viscose, adhesive, and acetylated cellulose, is substantially impervious to oils and greases. However, such a carton is not totally impervious to the passage of water, alcohol, or similar liquids. I accordingly prefer to employ a surface treatment on the finished carton which will provide the additional liquidproofing to render the carton totally impervious to liquids of the above mentioned type. The

' continuation of my method therefore comprises sheets are fed into the ate, a soap that the use of animal glues give superior results since although their inherent grease-proofing properties are low, addition of a plasticizing agent such as glycerol in varying quantities tends the total regeneration of all of the remaining viscose by any of the well known methods pointed out hereinbefore.

To either the inner and outer'surfaces of the completed container, or to both of these surfaces, I then apply an aqueous solution of an alkali soap of the fatty acids. These soaps may constitute either sodium, potassium, or ammonium compounds or other alkaline soaps of the fatty acids which are soluble in water. These salts may be salts of stearic, oleic, palmitic, or any of the other well known fatty acids. Upon the surfaces of the container thus'treated, I apply either immediately or after the lapse of whatever time may be required by manufacturing considerations, an aqueous solution of a metallic salt such as aluminum or zinc chlorides or sulphates. This latter heavy metal salt solution reacts with the previously applied soap solution to deposit a metallic soap in finely divided state, and since the reaction actually takes place in the pores and interstices in the surface layers of the carton material, these soaps are dispersed throughout the surface of the external regenerated cellulose film 4 as well as providing a water repellant outer coating 8. -I may, for example, apply to the carton an aqueous solution of potassium or sodium stearate and follow that with a solution of zinc chloride, or other zinc or aluminum salt. The alkali stearate and the zinc chloride react within the pores and interstices of the film 4 to precipitate zinc stearate or aluminum stearwhich is insoluble in water, alcohol, vegetable oils and greases and which is highly resistant to the action of dilute acids.

While I have' referred to my method of preparing paper containers as a means for providing a grease-proof paper container or as a means for grease-proofing materials, it is to be understood that the term is used, generically and refers to a means for providing a coating for such materials which is substantially impervious to water, oils, greases, and any of the liquids stated hereinabove since it has been found that a paper treated in the manner described to provide surface coatings of the type illustrated. in Fig. 1 is for all practicable purposes totally impervious to the passage of oils, greases and liquids of this type.

It will be observed that the treatment provided by the method of my invention tends to render 'the container so treated totally impervious by providing no less than eleven liquid resistant proofing'properties; for example, by impregnating the sheets I and 2 with viscose, feeding these sheets into the carton forming machine before the viscose sets or hardens and interposing between the sheets a suitable adhesive either with 5 time to harden and set, since when the viscosei r,

hardens the sheet becomes rigid and unpliable and impossible to use in this type of manufacturing process.

Certain other simplifications and modifications of my method may also be employed; for example, the surface treatment of'thecarton to provide the metallic soap dispersion in the outer regenerated cellulose layers may be eliminated whenever the carton is to have only oil proofing properties and neednot necessarily be impervi- 20 ous to all of the other liquids which I have mentioned hereinbefore. 7'

.The method of my invention may also be modified to provide a method of treatingpaper stock which is to be later used in the manufacturing of paper cartons such as cake boxes and the like fortreating other single layer porous materials prior to their use in manufacturing processes in contra-"distinction to the previous methwherein the treatment occurs substantially siultaneously with the manufacturing operations. have illustrated in Fig. 2 the appearance of n enlarged cross-section of a single sheet of pous materialB which has been treated on the {method This method is a derivation of the previously described method of manufacturing paper cartons and is based on the same fundamental principles. In this case I prefer to apply to the upper surface of the sheet 9 a relatively 43 thin layer of adhesive material II) which must be of such type as to provide adherence between the upper surface of the sheet 9 and a superimposed layer ll of viscose. I prefer to employ as the adhesive l0 an adhesive of the type de- .scribed hereinbefore operating also as a vehicle for carrying a suitable acetylating agent so that there is formed between the films l0 and H a very thin film I! of acetalized cellulose.

After the viscose 'film II is applied to the adhesive ID, the viscose film is completely regenerated by any of the known methods to provide a surface coating which is totally impervious to oils and greases and which has great flexibility The flexibility of regenerated cellulose to provide a coating which is totally grease-proof in the sense used in this specification. It is apparent, of course, that if found desirable this same treatment may be applied to both surfaces of the sheet 8 to provide additional protection against the passage of 7 greases and other liquids.

v This method of treatment may be further simplified in certain cases by omitting the acetylating agent from the adhesive l0, it being found that the thin layer 1| of regenerated cellulose ,It will be noted, however, that the funda- 10 pper surface thereof only by my alternative 40 secured to the surface of the sheet 9 by means of the flexible adhesive III also provides substantial grease-proofing properties.

While I have shown and described the preferred embodiment of my invention as applied to the preparation of paper for the manufacture of paper containers, it is tobe understood that I v comprehend the use of my method for.greaseproofing other materials such as cloth, wood,

concrete or cementitious materials and that the material so treated may beemployed for the manufacture of any of the diiferent things forwhich these materials are adapted and that the method of my invention may be employed either during the manufacture of the product orprior Y to the manufacture or may be applied as a treatment to the product after the manufacturing op .eration is completed, and I do not desire to be limited to any of the details shownor described herein, except as defined in the appended claims.

I claim: I I 1. The method of grease-proofing porous materials, comprising: applying, to the surface of Y said material a film of water soluble adhesive carrying an agent of the group consisting of acetic acid, nitric acid, and the water soluble salts of such acids; and applying a viscose film to said adhesive film to form an intermediate layer of a cellulose compound of the group con 'sisting of cellulose acetate and cellulose nitrate.

2. The method of grease-proofing porous materials, comprising: applying to the surface of said material a film of water soluble adhesive carrying an agent of the group consisting of acetic acid, nitric acid, and the water soluble salts of such acids; and establishing upon said adhesive film, a film ofvregenerated cellulose to form anvintermediate layer of a cellulose compound of the group consisting of cellulose ace.- tate and cellulose nitrate.

3. The method of grease-proofing porous materials, comprising: applying to' the surface of said material a film of water soluble adhesive carrying an agent of the group consisting of acetic acid, nitric acid, and the water soluble salts of such acids; applying a film'of viscose to said adhesive film to form an intermediate layer of a cellulose compound of the group consisting of cellulose acetate and cellulose nitrate; and regenerating said viscose film. Y

4. The method of grease-proofing porous ma terials, comprising: applying to the surface of said material a film of water soluble adhesive carrying an agent of the group consisting of acetic acid, nitric acid, and the water soluble salts of such acids; applying a film of viscose to said adhesive film to form an'intermediate layer of a cellulose compound of the group consisting of cellulose acetate andcellulose nitrate; and regenerating said viscose film by the application of heat.

5. The method of grease-proofing porous materials, comprising: applying to the surface of said material a film of water soluble adhesive carrying anagent of the group consisting of acetic acid, nitric acid, and the water soluble salts of such acids; applying a film of viscose to said adhesive film to form an intermediate layer of a cellulose compound of the group'consisting of cellulose acetate and cellulose nitrate; regenerat ing said viscose film by aging; and washing said regenerated cellulose film to remove free sulphur compounds normally present therein.

10. The method of grease-proofing porous mamaterial a film of water soluble adhesive carrying an agent of the group consisting .of acetic acid, nitric acid, and the water soluble salts of such acids; applying a film of viscose to said adhesive film to form an intermediate layer of a cellulose compound of the group consisting of cellulose acetate and cellulose nitrate; regenerating said viscose film by applying dilute solutions of the inorganic acids to the surface thereof; and washing said film to remove excess acid.

'7. The method of grease-proofing porous materials, comprising: applying to the surface of said material a film of water soluble adhesive carrying an agent of the group consisting of acetic acid,

nitric acid, and the water soluble salts of such.

acids; applying a film of viscose to said adhesive film to form an intermediate layer of a cellulose compound of the group consisting of cellulose acetate and cellulose nitrate; regenerating said viscose film by applying dilute solutions of the inorganic acids to the surface thereof; neutralizing excess acid with alkaline solutions; and washing said film.

8. The method of rendering porous materials impervious to a liquid, comprising: establishing upon the surface of said material a film of regenerated cellulose; and precipitating in the pores of said regenerated cellulose film a metallic soap in-. soluble in said liquid.

9. The method of rendering flexible porous materials impervious to a liquid while retaining a degree of flexibility that will permit fabricating the finished product into containers or boxes, comprising: establishing upon the surface of said material a film of flexible bonding adhesive and superimposing upon said film a film of regenerated cellulose, and precipitating in the pores of said regenerated cellulose film, an insoluble metallic soap.

terials, comprising: establishing upon the surface of said material a film of regenerated cellulose; applying to said surface film an aqueous solution of an alkaline soap of a fatty acid; and applying to the surface so treated an aqueous solution of a metallic salt to deposit in the pores of said regenerated cellulose film an insoluble metallic soap.

11. The method of grease-proofing a container manufactured from porous materials, comprising: impregnating said container material with viscose; regenerating said viscose; applying to the surfaces of said container an aqueous solution of an alkaline soap of a fatty acid; and then applying .to the surfaces of said container an aqueous solution of a metallic salt to form an insoluble metallic soap dispersed in the pores of said regenerated cellulose.

12. The method of grease-proofing porous materials, comprising: applying to the surface of said material a film of flexible water soluble adhesive carrying an agent of the group consisting of acetic acid, nitric acid, and the water soluble salts 'of such acids; and applying a viscose film to said adhesive film to form an intermediate layer of a cellulose compound of the group consisting of cellulose acetate and cellulose nitrate.

13. The method of grease-proofing porous materials, comprising: applying to the surface of said materials a film of water soluble adhesive carrying an admixed plasticizing agent and. an agent of the group consisting of acetic acid, nitric acid, and the water solublesalts of such acids; and applying a viscose film to said adhesive film to form an intermediate layer of a cellulose compound of the group consisting 'of cellulose acetate and cellulose nitrate.

ALBERT A. ROBBINS. 

